1. Field of the Invention
The present invention relates to methods of wiring formation and manufacturing electronic components, and more specifically, it relates to methods of fine wiring formation using a semi-additive process.
2. Description of the Related Art
In semiconductor integrated circuits, semiconductor devices, wiring substrates, etc., fine and low-resistance wiring patterns are necessary. Therefore, an aspect ratio (wiring thickness/wiring width) of the wiring pattern must be large. In order to form a wiring pattern having a high aspect ratio, a semi-additive process has been generally used.
A method of formation of the wiring pattern by the conventional semi-additive process is shown in FIGS. 1A to 1D. A feeder film 22 is formed on the entire surface of the substrate 21, thereafter a photoresist is coated thereon. Then, the photoresist is patterned to form a resist pattern 23, for a selective electrolytic plating, on the feeder film 22 as shown in FIG. 1A. As the feeder film 22, generally, a two-layer film composed of an upper layer made of Cu and a lower layer made of Ti, is used in the case of Cu plating, and an upper layer made of Pd and a lower layer made of Ti, is used in the case of Au plating.
Then, by immersing the substrate 1 into an electrolytic plating solution, and passing a current through the feeder film 22 as an electrolytic plating electrode, as shown in FIG. 1B, the plating metal is deposited on the feeder film 22 in an area exposed from the resist pattern 23, and a plated wiring 24 is formed. After the completion of the electrolytic plating, the substrate 21 is washed, then, the resist pattern 23 is peeled away as shown in FIG. 1C.
Thereafter, by completely etching the feeder film 22 exposed from the plated wiring 24, the wiring pattern, having a desired pattern, composed of the feeder film 22 and the plated wiring 24 as shown in FIG. 1D is obtained.
In the aforementioned method of fine wiring formation, as shown in FIG. 1D, the exposed portion of the feeder film 22 is removed by the etching after forming the plated wiring 24, and dry etching or wet etching methods are used.
The dry etching methods include ion milling, reactive ion etching (RIE), and others. By using these methods, it is possible to form the fine wiring pattern in which the line and space (hereafter described as L/S) is 5 μm or less.
In the dry etching methods, however, expensive apparatuses are required, and therefore, the manufacturing cost is very high. Furthermore, in the ion milling, it is not possible to selectively etch only the feeder film, but the plated wiring and the substrate are etched together with the feeder film so that problems of etching residues and substrate damage occur. In the reactive ion etching, there is a problem in that a suitable material for the feeder film has not been identified.
On the other hand, in the wet etching methods, hydrofluoric acid is used in the case of the feeder film made of Cu or Ti, and a mixture of nitric acid and hydrochloric acid is used in the case of the feeder film made of Pd. The wet etching methods is very low in the cost compared to the dry etching methods, and it is easy to selectively etch only the feeder film.
Because the wet etching is isotropic, however, when the feeder film 22 is wet etched, as shown in FIG. 2, the feeder film 22 under the plated wiring 24 is also side-etched to cause an undercut 25 under the plated wiring 24 so that defects such as insufficient adhesion and peeling of the wiring may be caused. Therefore, in the wet etching, there is a limit in accuracy at L/S=5 μm to 10 μm, and then a fine wiring in which the L/S is 5 μm or less could not been obtained.